Underwater propulsion systems employing n2o



March 4, 1969 L. GREINER 3,430,602

UNDERWATER PROPULSION SYSTEMS EMPLOYING N 0 Filed Feb. 16, 1967 Sheet LEONARD GREINER INVENTOR.

ATTORNEY March 4, 1969 L. GREINER 3,430,602

UNDERWATER PROPULSION SYSTEMS EMPLOYING N 0 Filed Feb. 16. 1967 Sheet Q of 2 47 5455' u 53 i2 48 g} 53 REINER INVENTOR.

United States Patent 3,430,602 UNDERWATER PROPULSION SYSTEMS EMPLOYING N Leonard Greiner, Palo Alto, Calif., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Feb. 16, 1967, Ser. No. 616,530

US. Cl. 115-6.1 Int. Cl. B63c .11 /00; A63b 35/00 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to underwater propulsion systems for swimmers in which nitrous oxide is used as a monopropellant.

Various attempts have been made to provide swimmer propulsion units which may be used to increase the swimmers underwater speed, range and maneuverability. These systems employ various power sources including gas sources, employing pressurized gas; and monopropellant and bipropellant systems; as Well as electrical power sources such as batteries.

Representative systems are described in US. Patents 3,090,345; 3,048,140; 3,034,467; 3,014,448; 3,128,739; and 3,136,279. Such systems are either quite bulky and complex or lack power and endurance. It has been found, however, according to this invention, that a light weight, simple and high power density propulsion unit can be obtained when nitrous oxide is used as the propellant. In addition, by proper treatment of the working fluid, it is possible to obtain both a gaseous mixture which may be used for breathing purposes by the swimmer and hot water that can be used to heat the suit of the swimmer.

It is accordingly an object of this invention to provide a compact, self-contained underwater swimmer propulsion unit.

It is another object of this invention to provide an underwater propulsion system that provides a breathable exhaust.

It is another object of this invention to provide an underwater propulsion unit that generates hot water for use in heating a swimmers suit.

It is another object of this invention to provide an underwater propulsion system employing N 0 as the propellant.

These and other objects of this invention will be readily apparent from the following description with reference to the accompanying drawings wherein:

FIGURE 1 is a side view of an embodiment of this invention being worn by a swimmer.

FIGURE 2 is a schematic view partly in section of another embodiment of this invention.

Referring now to FIGURE 1 a swimmer 1 is shown having an underwater propulsion system according to this invention carried on his back by means of straps 2. The system comprises a tank 3 of liquid N 0 connected to decomposition chamber 4 by flow control valve 5 and line 10. A resistance element 7 extending within decomposition chamber 4 is provided which may be heated to red heat by battery pack 6 upon actuation of switch 8. The decomposition chamber feeds hot gases into prime mover 3,430,602 Patented Mar. 4, 1969 9 which may be tur-bine or reciprocating engine and the gases are dumped overboard through duct 12. A check valve may be employed in duct 12, if necessary, to prevent ambient Water from entering prime mover 9 if the power plant is stopped under water. Prime mover 9 in turn drives the propulsive means 11. Means 11 is illustrated as being a pump which takes water in through duct 13 and exhausts a stream of water through duct 14 to produce a reaction propulsive thrust but it should be recognized that means 11 could also be any other conventional propeller or other propulsive device such as, for example, a propeller driven through suitable transmission means by prime mover 9.

In operation, resistance element 7 is heated upon actuation of switch 8 and N 0 is fed into decomposition chamher 4 where it contacts the heated resistance element 7 and decomposes into primarily N and 0 at about 1600" C. Once decomposition has started, the switch can be thrown to the olf position and decomposition of subsequently injected N 0 into the chamber will continue upon contacting the hot-gas environment. The output of the system can be regulated by the setting of valve 5.

In this system, N 0 has a distinct advantage over conventional monopropellants such as H 0 in that at ambi ent conditions the vapor pressure of liquid N 0 is sufliciently high as to obviate any need for additional pressurization to feed the propellant into the decomposition chamber. Also N 0 is quite inexpensive and safe. It is not corrosive so the materials it contacts can be conventional. Also it is stable and does not tend to decompose.

The system of FIGURE 1 provides a compact propulsion system but requires an additional oxygen source for the swimmer. Since the exhaust gases consist primarily of about 67% N and 33% 0 by volume, it would appear that they could be used for breathing purposes. It has been found, however, that at the equilibrium decomposition temperature of N 0 of about 1600 C. toxic quanties of N0 of about 5,000 p.p.m. are contained in the gaseous mixture. The gases therefore can only be used for breathing if the NO content can be reduced to the nontoxic level of below 50 p.p.m. Referring now to FIG- URE 2, a self-contained breathing and propulsion unit is shown. The unit comprises a tank of liquid N 0 20, and a streamlined casing 21 containing the components of the propulsion and breathing system.

These components comprise a decomposition chamber 22 which feeds hot gases to turbine 23 which drives a two stage pump 24. The high pressure stage 24a delivers high pressure water obtained from the sea through inlet 29 to heat exchanger 25 and centrifugal separator 26 through lines 27 and 28. Stage 24!) of two stage pump inducts water through inlet 30 and exhausts a propulsive jet of water through outlet 31 which jet provides the propulsive force for the system.

Means should be provided for inactivating stage 24b to permit the system to be operated underwater without producing any propulsive force so that breathing air may be generated while the swimmer remains stationary or moves at low speed. Such means may comprise valve 32 in the inlet for stage 24b which can cut off the supply of water to stage 24b. In the alternative, clutch means, for example, could be employed to disconnect stage 24b from stage 24a.

The exhaust gases from the turbine pass through line 33 to heat exchanger 25 where they are passed in countercurrent heat exchange with the water from line 27 and are fed through line 34 to centrifugal separator 26. The water from line 27 after passing through heat exchanger 25 is divided into two lines 35 and 36. Line 35 may be connected to the suit of the swimmer to provide hot water for circulation therethrough for heating purposes. Line 36 feeds into decomposition chamber 22 as will be more fully explained below.

The centrifugal separator 26 separates the gaseous and liquid components of the material in lines 34 and 28 and also washes the gas in line 34 with water from line 28. The liquid eflluent may be supplied to the suit of the swimmer for heating purposes or may be dumped overboard through outlet 37 which may be provided with check valve 38 and the gaseous efiluent is passed through line 39 to accumulator 40. Accumulator 40 is provided with a pressure relief valve 41 in outlet 42 for venting of excess gases. Outlet 43 is also provided which is adapted to be connected to a flexible supply line 44 which feeds gas to the conventional pressure regulating valve and face mask assembly used in underwater breathing apparatus which is not shown and forms no part of this invention.

The N tank is connected to decomposition chamber 22 by line 45 and control valve 46. A resistance element 47 is also located in decomposition chamber 22 and is energized by battery pack 48 which causes a current to flow through resistance element 47 and wires 48 upon activation of switch 49. Pack 48 is adapted to be carried on the belt of the swimmer. A hand pump 50 is also provided which supplies water to stage 24a for start-up purposes through line 51 and check valve 52. Loops 53 are also provided for straps to aflix the system to the back of a swimmer or to a suitable support which may be grasped by the swimmer to tow him through the water.

In order to operate the system the swimmer would at least partially submerge the device so that pump 50 and inlet 29 are within the water. Valves 32 and 46 are closed and switch 49 would be thrown to energize the resistance element 47. Pump 50 would be actuated to start water flowing through stage 24a, lines 27, 28, 35, and 36 and to introduce Water into decomposition chamber 22. Valve 46 would then be opened to permit flow of N 0 to decomposition chamber 22 wherein the N O decomposes to N and 0 upon contact with the hot resistance element 47. The hot decomposition gases cause the water from line 36 to vaporize and the working fluid consisting of essentially N 0 and steam energize turbine 23. The switch 49 may be thrown to the off position at this point and the decomposition of N 0 will continue by heat exchange mechanisms within the decomposition chamber 22.

As was noted above, the decomposition of N 0 at equilibrium temperatures at 1600 C. produces toxic quantities of N0 of about 5,000 p.p.m. However, it has been determined that if the temperature within decomposition chamber is maintained at or below 750 C., the NO content is reduced to or below 50 p.p.m., the nontoxic upper limit. In order to maintain this temperature stage 24a and lines 28, 35, and 36 should be designed to supply to chamber 22 about 0.65 mole of water for each mole of N 0 fed thereinto. After passing through turbine 23, the working fluid is cooled in heat exchanger to condense the steam and to cause NO to react with O to form N0 which dissolves in the condensed steam. This additional reaction further reduces the NO content of the working fluid. The mixture then passes into separator 26 wherein the gaseous and liquid components are separated and the gases are washed with additional water from line 28. The liquid eflluent which is dilute aqueous HNO and HNO is dumped overboard or may be supplied to the suit of the swimmer for heating purposes.

The gases in accumulator 40 are fed into line 44 connected to the swimmers breathing apparatus and if more breathing gas is being generated than can be stored in accumulator 40 or consumed by the swimmer, the excess is vented overboard through line 42. For propulsion purposes, valve 32 would be opened permitting water to pass through stage 24b producing a propulsive jet from duct 31. The velocity can be controlled by the setting of valve 32 or by the setting of valve 46.

The theoretical energy available from the system of FIGURE 2 if tank 20 is about 24" long and 8" in diameter is approximately 2.5 HP hrs. Assuming a 40% efliciency in conversion to thrust about 1 HF. hr. is available for propulsion. The practical speed limit for underwater swimmers not enclosed in a fairing is between 4 and 5 knots and about /2 horsepower is required at these speeds. Thus, the instant system could propel a swimmer at maximum speed for about 2 hours. Of course, at lower speeds the duration would be greatly extended. With respect to breathing, about 2.4 pounds of oxygen pass through a swimmers lungs per hour. The tank contains about 7.3 pounds of oxygen in the N 0 thus about 3 hours of breathing gases are available if the breathing gases are not recirculated.

In this example, the minimum power output of the system is determined by the breathing gas requirements and under some circumstances, it may be desired to move at a speed slower than that which would be produced at this power level. Under this condition valve 46 would be set to produce adequate breathing air and valve 32 could then be adjusted to restrict or shut off the flow of water to stage 24b, thus permitting infinite variation in thrust from zero to the maximum while generating sufiicient amounts of breathing gas.

It should also be noted that substantially more water must be circulated through heat exchanger 25 to condense the steam in the turbine exhaust than is required for introduction into decomposition chamber 22 and separator 26. Thus, substantial amounts of hot water are available from line 35 for circulation through the swimmers underwater suit for body heating purposes.

While the power plants of this invention have been illustrated as being mounted on the swimmer it is readily apparent that other means of transmitting the propulsion force to the swimmer could be employed. For example the power plant could be mounted on a suitable support or framework which would be grasped by the swimmer and which would tow the swimmer through the water.

This invention has been described with respect to various embodiments thereof. These embodiments are illustrative rather than limiting and modifications thereto can be made without departing from the scope of this invention.

I claim:

1. A method of swimmer propulsion which comprises decomposing N 0 in the presence of an amount of water suflicient to maintain the equilibrium temperature of the decomposition reaction below 750 C., generating propulsive force from the decomposition products-steam working fluid so produced and supplying at least a portion of said decomposition products to said swimmer for breathing purposes.

2. The method of claim 1 wherein the NO content of said decomposition roducts is maintained below 50 p.p.m.

3. The method of claim 1 wherein said N 0 is decomposed in the presence of at least 0.65 mole of water for each mole of N 0 to produce a working fluid comprising N 0 and steam, generating propulsive force from said working fluid, condensing said steam, separating said N and 0 from said condensed steam and feeding said N; and O to the swimmer for breathing purposes.

4. A combined breathing and propulsion unit for an underwater swimmer comprising:

(a) a source of N 0 (b) means for decomposing said N 0 (0) means for generating a working fluid by mixing the decomposition products of said N 0 with water to produce a working fluid consisting primarily of N 0 and steam (d) means for generating a propulsive force from said working fluid (e) means for separating said N and 0 from said working fluid and (f) means for supplying said N and O to said swimmer for breathing purposes.

5. The unit of claim 4 further comprising means for varying the propulsive force independently of the rate of generation of said working fluid whereby N and 0 for breathing purposes may be generated while said swimmer is stationary or moving at low speeds.

6. The unit of claim 4 further comprising:

(a) heat exchange means for condensing the steam in said working fluid by heat exchange with a stream of water (b) means for supplying a portion of said water heated in said heat exchanger to said means for generating a working fluid and means for supplying the remainder of said heat water to the suit of said swimmer for heating purposes.

7. The unit of claim 4 wherein said means for generating a working fluid maintains an equilibrium temperature of no greater than 750 C.

8. The unit of claim 7 wherein said equilibrium temperature is maintained by introducing into said means for generating a working fluid at least 0.65 mole of H 0 for each mole of N 0 decomposed.

9. A propulsion unit for underwater propulsion of a swimmer comprising:

UNITED STATES PATENTS 3,293,851 12/1966 Hulbert et a1 115-61 X OTHER REFERENCES Elder, Scott and Kanda, Textbook of Chemistry, 1948.

TRYGVE M. BLIX, Primary Examiner.

US. Cl. X.R. 204, 218 

